The present invention relates to an improved ion implantation apparatus. More particularly, the invention concerns an ion implantation apparatus in which multiple ion beams of predetermined spot size are focused upon discrete chip areas of a traget wafer whereby simultaneous implantation of such chip areas can be achieved.
In the usual ion implantation apparatus, a single beam of ions is deflected in a predetermined pattern or scanning mode to successively cover multiple chip areas upon a target wafer, whereby each of the chip areas eventually receives a prescribed dosage or implantation of ions. Such implantation steps are used, for example, in the production of microelectronic devices. However, in the microfabrication of large numbers of devices, the utilization of a single ion beam and a progressive scanning arrangement require a significant expenditure of time.
Accordingly, a need exists in ion implantation technology, as it is applied to the microfabrication of electronic devices, for an implantation apparatus capable of simultaneously carrying out the implantation step with respect to multiple chip areas defined upon a target wafer.
It should be recognized that multiple electron beams have been utilized heretofore in the prior art. For example, U.S. Pat. No. 3,770,934 to Randmer describes an electron beam heating apparatus for heating large workpieces by electron bombardment, which includes means for forming and beaming a plurality of electron beams. In addition, U.S. Pat. No. 3,394,217 to Fisk describes a method and apparatus for controlling plural electron beams, where a target material confined within a crucible is heated by bombardment with such beams. It should be apparent that the requirements of systems for electron beam heating are significantly different from the requirements for control of ion beams in connection with ion implantation apparatus, however.
In addition, U.S. Pat. No. 3,491,236 to Newberry discloses an apparatus useful in fabrication of microelectronic circuit patterns by means of applying electron beam patterns to a target 13 to expose successive portions of the target. A matrix illustrated in FIG. 5 is provided to control the deflection of the electron beam to successive target areas. The matrix is constructed of a plurality of "lenslets", with each "lenslet" being adapted to control the impingement of a main electron beam on a given area of the target.
There is a suggestion in the Newberry disclosure that the main electron beam could be utilized to flood a plurality of "lenslets" at one time and thereby impinge upon plural target areas simultaneously. There is a further suggestion by Newberry that the invention could be utilized to control an ion beam rather than an electron beam, if desired. However, it should be apparent that certain inherent limitations of the Newberry system would preclude its effective use in connection with ion implantation apparatus. Thus, the Newberry matrix, utilizing a plurality of "lenslets", results in overlap of electron exposure from several adjacent "lenslets" onto any given target area. This precludes the necessary resolution required for ion implantation.
Moreover, it should be recognized that the effects of space-charge in an ion beam are more pronounced than spacecharge effects occurring within an electron beam. Accordingly, the use of a planar matrix such as that disclosed by Newberry would be inadequate to maintain control of a plurality of individual ion beams, due to the more pronounced effects of space-charge in the ion beam system.
Other systems are known which utilize aperture plates having multiple apertures formed therein to produce ion beams of wide diameters through the merging of plural beamlets emitted from the aperture plate into a single beam. Such systems have been used for ion beam machining and the like, where there was apparently no need to maintain a plurality of discrete beams.